The Dual Probe Concealed Information Test

Few countries has applied the Concealed Information Test(CIT)in the field,the mainly limitation is that the innocent people with crime-related information(i.e.,knowledgeable innocent)are liable to be misjudged as guilty.Thus,it is urgent to develop some effective methods that can distinguish between the guilty and the knowledgeable innocent.The Complex Trial Protocol is effective and countermeasure-resistant but has been reported to be vulnerable to lead to chance false positive when presenting only one probe items per trial.The dual probe complex trial protocol(DPCTP)can reduce the false positive rate.In addition,the guilty person knows the crime very well,while the knowledgeable innocent person only has a small amount of crime-related information.Thus,this study aims to explore the discrimination of the guilty and the knowledgeable innocent when using DPCTP with P300 index based on their different levels of crime-related information knowledge.This plays an important role in the quick determination of criminal suspects and the timely emlimination of innocent person in criminal cases.We conducted two experiments to explore above issues.The experiment 1 includes two Blocks,Block1 is DPCTP,which is divided into two stages.In stage1(S1),participants were instructed to do a perception acknowledgement response with probe and irrelevant items.In stage2(S2),participants were required to do the stimulus discrimination task with probe,irrelevant,and target stimli.Blcok2 is r DPCTP(reversed-Dual Probe Complex Trial Protocol),which required participants to complete the discrimination task in S1 and the perception acknowledgement task in S2.The results showed that the DPCTP has better detection effect when dual probe items were used to reduce the false positive rate and subject fatigue.On the basis of experiment 1,the DPCTP with better detective effects employed in experiment 2,in which different crime-related information was presented in different stage.In S1,the crimerelated information that the guily knew,the knowledgeable innocent and unknowledgeable innocent didn’t know was presented.In S2,the crime-related information that the guilty and the knowledgeable innocent knew and the unknowledgeable innocent didn’t know was presented.The results showed that when using the average number of the two stage’s bootstapped iterations in 1000 with probe > irrelevant for individual diagnosis,DPCTP could not only effectively distinguish the guilty from the unknowledgeable innocent,but also distinguish the guilty from the knowledgeable innocent(AUC = 0.88).